1. Field of the Invention
Methods and apparatuses consistent with the present invention relate to scanning for an idle channel, and more particularly, to scanning for an idle channel in the same frequency environment.
2. Description of the Related Art
A technology related to a cognitive radio technology for sensing a current state of a channel according to region and time, intelligently determining the current state, selecting an appropriate frequency, modulation, and output power, and dynamically moving to an idle channel to perform radio communication in real time, has been actively developed so as to use limited frequency resources.
In order to use such technology in an ultra high frequency (UHF) band, it is important that the technology is capable of rapidly detecting a primary user device (i.e., a device which has priority to use a channel), and allows communication between devices other than the primary user device, by using an idle channel that is a channel not used by the primary user device.
FIG. 1 is a diagram illustrating a conventional method of scanning frequencies to obtain a channel state.
In operation 110, a base station transmits a channel state scanning request to a terminal.
Although FIG. 1 shows a single terminal, the base station may transmit a channel state scanning request to a plurality of terminals. Hereinafter, a process will be described as if performed between one of a plurality of terminals and the base station.
In operation 120, the terminal transmits a request received response to the base station, indicating that the terminal has received the channel state scanning request. If the base station does not receive the request received response, the base station again transmits the channel state scanning request to the terminal. If the base station received the response, the base station waits for a report of the channel state from the terminal.
In operation 130, the terminal reports the channel state scanned according to the channel state scanning request, to the base station.
In operation 140, the base station transmits a report received response to the terminal, indicating that the base station has received the channel state report from the terminal. If the terminal does not receive the report received response, the terminal again reports the channel state to the base station.
The base station receives a channel state report from the plurality of terminals according to the above process. Each channel state report includes information regarding the communication quality of the channel, and whether the channel is in use.
At this time, each terminal scans the state of all frequency channels within its surrounding environment (i.e., its frequency environment) and reports each channel state to the base station. Conventionally, since the plurality of terminals are far away from each other (e.g., 30˜100 km), the frequency environment of each terminal differs from that of another terminal, so that the base station receives different information regarding the channel state from each terminal.
However, when the frequency band is a UHF band, each terminal can have the same frequency environment due to the characteristics of a UHF radio wave in a small area, for example, indoors. As such, the conventional method has a problem in that each of a plurality of terminals scans the state of all frequency channels in the same frequency environment, and thus the conventional method cannot efficiently scan the frequency environment to obtain the state of all the frequency channels.